It is proposed to study the mechanisms underlying the synthesis of the rheumatoid factors and the significance of IgG rheumatoid factor in the systemic complications of rheumatoid arthritis. The synthesis of IgG and IgM rheumatoid factors by circulating peripheral blood mononuclear cells will be examined and the mononuclear cell types involved will be investigated. Other modifying factors will also be examined. Synthesis of rheumatoid factor will be measured by a radioimmunoassay method. The IgG and IgM rheumatoid factor content of sera of patients with rheumatoid arthritis and particularly of those with the systemic complications of rheumatoid arthritis will be measured using a radioimmunoassay method. To further evaluate the role of IgG rheumatoid factor in the systemic complications of rheumatoid arthritis, complement levels, Clq binding levels, monoclonal rheumatoid factor binding assays and ultracentrifugation of sera for intermediate complexes will be measured.